I agree that a complete and thorough determination is still a way off.
It is my understanding that increasing CO2 in the atmosphere reaches a saturation point, a point that after which you can add all the CO2 you like to the atmosphere and it will not increase temperatures any further. It is my understanding that the maximum warming that could occur with additional CO2 is about 1 degree celsius. You could take CO2 all the way to 6000ppm at which point it would become letahl to humans and you would still only have the one degree of warming.
Correct me if I am wrong, but I don't believe I am.